The invention relates to an antenna diversity system for radio reception in vehicles, which comprises a receiver, two antennas, with antenna feed lines connected to an antenna diversity module. The diversity module is connected with the receiver by way of a receiver line, on the output side, and an evaluation circuit, which evaluates the interference in a reception signal just arriving at the receiver.
An antenna diversity system of this type is preferably used for ultra-short-wave radio reception, and is known from DE 102 005 403 304. Particularly in the case of an ultra-short-wave radio reception system, which is part of the standard equipment of vehicles, for the most part, the efficiency of the system is of particular importance. The advantages achieved with antenna diversity systems of this type are mainly in the creation of a particularly economical solution with regard to a good desired signal/interference signal ratio, also with regard to same-channel or adjacent-channel interference. These advantages allow the system to be configured for a plurality of antennas, while simultaneously minimizing the amount of cables in the vehicle. If the antenna diversity module is in the vicinity of a compact multi-antenna system, for example, such as on the rear window of a vehicle, only one receiver line to the receiver is required even when there are a plurality of antennas.
However, with an antenna diversity system according to the previously known patent application, it is too complicated or it is impossible to use the plurality of the antennas provided, in most cases four, in order to achieve sufficient diversity efficiency. In these cases, it is desirable to improve the diversity efficiency that can be achieved with the small number of antennas such as only two antennas, particularly with regard to reducing adjacent-channel interference. This form of interference has become dominant, particularly in the ultra-short-wave radio frequency range, because of the great increase in the number of new radio stations, and the resulting frequency channels of the radio stations, which partially overlap in border regions.